It's impossible to discuss The Dark Knight without bringing up Heath Ledger. Ledger's performance as The Joker is the first performance of 2008 to gather Oscar buzz. If in fact Ledger is honored by the Academy for his portrayal of the twisted character, then he would be the first actor to receive an Academy Award posthumously since Peter Finch won for Best Actor in 1976's Network.
Sadly, Ledger passed away while The Dark Knight was in post-production. Many members of the media, and the general public, speculated that playing The Joker affected Ledger so deeply that it contributed to his death. Asked to address that, Nolan replied, "I'll answer that simply to say that it diminishes his skill as an actor. The job of an actor is someone who takes on a character and distinguishes between real life and a character. Anyone who's spent time on a movie set knows that it's a very artificial environment and the great skill of someone like Heath Ledger or Christian Bale, all these guys, is that they can be jobbing along in a workaday environment and then when the camera rolls they can find this great character."
"I'm very confident that the performance has been edited exactly as it would've been had Heath not died," said Nolan about dealing with the loss of one of the film's stars after shooting had wrapped. "It was very important to me that his performance be put out there exactly the way that we had intended it and that he had intended it to be seen as well. Watching him come up with the characterization was a pretty exciting and pretty amazing thing because you're looking at an actor craft an iconic presence for a character, but making it human at the same time. That's an incredible thing to do and the way in which he's done it is extraordinarily complicated."
"Everything about what he does from every gesture, every little facial tick, everything he's doing with his voice – it all speaks to the heart of this character. It all speaks to this idea of a character who's devoted to a concept of pure anarchy and chaos. It's hard to get a handle on how those elements combine. The physicality reminds me of the great silent comedians. It has a bit of [Buster] Keaton and [Charlie] Chaplin about it. The voice is very difficult to imitate. Every film set, on every crew there are dozens of talented mimics who are always taking off different performances or lines that they've heard from actors before, but no one could do The Joker. No one has been able to imitate it successfully. It's very elusive and complicated, but working with Heath you would see that he very precisely worked out every aspect of him. "
Nolan says Ledger talked to him throughout the process of getting into the character of The Joker. "Yeah, to a degree. When I was working on the script and he'd gone off to think about what he was going to do with the character, he would call me from time to time and talk about the things that he was working on. But the truth is that when you're outside that process before you get to set it's all a bit abstract. So he was talking to me about how he'd been studying the way that ventriloquist dummies talk and things like that. I'd be sitting on the other end of the phone going, 'Well, that's a bit peculiar.' But what I'm really hearing is an actor really invested in trying to come up with something very unique," explained Nolan. "Then when I saw it all come together, the conversations we'd had kind of made sense. I could see where he was coming from with that with the pitch of the voice."
"He would talk about having it change pitch dramatically in very sudden ways and things like that. That helps the unpredictability of the character. When we were mixing the sound for the film, we let his voice – normally you're sort of flattening out voices to make them clearer, evening out the volume at which they speak - but with The Joker we felt that you had to let it be a little bit out of control in the way that he performed it."
Ledger drew from a wide variety of sources to come up with his unique and definitive take on The Joker. "It's really a lot of different things mixed together," said Nolan. "Certainly visually, with the makeup, I always had the idea of Francis Bacon paintings and I showed those to Heath and showed those to John Caglione who did the makeup. We were looking at smearing and smudging and caking the makeup on him, doing it in ways that we could degrade the look through the film. But really I think what he's done is very unique. You can see different influences. You can see Alex in A Clockwork Orange. You can see a Francis Bacon paintings or the punk sort of influence, but I think there's a very unique combination that he's made from those."